Heyo,
I solved the problem. Strange, but by trial and error I found the troublemaker.
1. I am using four external HDs, one dedicated as storage for PT Sessions and Samples. And esp. this HD was the troublemaker, although no failure could be found on this HD with disk utility.
2. I renamed the known locations for my sessions and my samples on this external HD to see what happens. In the end, Pro Tools does not like the location of my Samples-Folder anymore that has been linked into to the Workspace/Sound Libraries-Locations. No idea why, because I did not change anything there.
3. So, I removed this Sound Library location from the Workspace only, but still using the old folder name for my samples and VOILA, it works now. No crash since then.
I thought, what the hell? A bug?
Maybe anyone will find this workaround helpful
Mike